1 - Introduction: Putnam's reflections on the brain in a vat

Summary

In 1981, Hilary Putnam published a paper entitled “Brains in a Vat.” In it, he reflected on a “science fiction possibility discussed by philosophers,” which he describes as follows:

a human being (you can imagine this to be yourself) has been subjected to an operation by an evil scientist. The person's brain (your brain) has been removed from the body and placed in a vat of nutrients which keeps the brain alive. The nerve endings have been connected to a super-scientific computer which causes the person whose brain it is to have the illusion that everything is perfectly normal. There seem to be people, objects, the sky, etc; but really all the person (you) is experiencing is the result of electronic impulses travelling from the computer to the nerve endings. The computer is so clever that if the person tries to raise his hand, the feedback from the computer will cause him to ‘see’ and ‘feel’ the hand being raised. Moreover, by varying the program, the evil scientist can cause the victim to ‘experience’ (or hallucinate) any situation or environment the evil scientist wishes. He can also obliterate the memory of the brain operation, so that the victim will seem to himself to have always been in this environment. It can even seem to the victim that he is sitting and reading these very words about the amusing but quite absurd supposition that there is an evil scientist who removes people's brains from their bodies and places them in a vat of nutrients which keep the brains alive. The nerve endings are supposed to be connected to a super-scientific computer which causes the person whose brain it is to have the illusion that … (Putnam 1981b: 5–6)

This scenario, which will henceforth be called the brain-in-a-vat (or BIV) scenario, has generated a tremendous amount of philosophical commentary in the more than three decades since its publication.

Putnam's reflections on the BIV scenario have a familiar historical precedent, of course, in Descartes's reflections on the Evil Demon scenario.